Selective Catalytic Reduction (SCR) systems have been employed for purification of harmful NOx components in the exhaust gases of diesel vehicles. The SCR systems use urea solution referred to as Diesel Exhaust Fluid (DEF) for purification of the exhaust gases. The urea solution is stored in a urea tank provided on the vehicles. It is essential to ensure appropriate composition and levels of the urea solution inside the tank to achieve efficient purification of the exhaust gases. Urea sensors are thus employed in the urea tanks for measuring the level and/or concentration and/or temperature of the urea solution in the tank. The urea sensor has a level measurement device, a concentration and/or quality measurement device, a temperature measurement device, a suction tube, and a return tube. The suction tube draws urea solution from the urea tank and provides it for breaking down the NOx in the exhaust gas. The return tube circulates any excess amount of urea solution back into the urea tank.
The urea solution has a freezing point of −11° C. Frozen urea solution can pose problems in efficiently breaking down NOx because high volume expansion of the urea solution due to freezing can result in excessive pressure generated inside the suction tube. In addition, due to these high pressures, there is a possibility of rupture of the suction pipe, of the fittings on the suction pipe, and other elements of the suction pipe. In other cases, this pressure may act downwards, forcing a filter on the urea sensor to move or break apart. Currently, there are no efficient solutions to overcome the problem of over pressure on the suction pipe due to freezing.
Korean Patent No. 101205234 discloses a urea solution tank for a diesel vehicle. To prevent ice from colliding with a sensor module, the lower parts of a heating pipe, suction pipe, level sensor, and quality sensor are inserted into a protector. The urea solution tank comprises a tank housing, a sensor module, and a protector. The sensor module comprises a heating pipe, a suction pipe, a level sensor, and a quality sensor. The heating pipe melts the frozen urea solution in the winter. The suction pipe supplies the urea solution to a urea solution sprayer. The level sensor measures the level of the urea solution by a float. The quality sensor measures the concentration and temperature of the urea solution. The lower parts of the heating pipe, suction pipe, level sensor, and quality sensor are inserted into the protector. The protector prevents ice from colliding with the sensor module. The melted urea solution flows down along an inclined portion, and the urea solution flows to the inlet of the suction pipe.
Korean Patent No. 102013005141 discloses a vertical pipe for electrically melting a frozen urea solution. A flexible heating member is provided to rapidly melt the frozen urea solution by independently controlling temperature by a temperature control unit. The vertical pipe for electrically melting the frozen urea solution comprises flexible heating members, a filler member, a urea solution suction pipe, and a urea solution return pipe. The flexible heating members are arranged in a space between an outer pipe and an inner pipe along the length of the vertical pipe at constant intervals. The flexible heating member is filled with the filler members. The urea solution return pipe is shorter than the urea solution suction pipe. The urea solution return pipe and the urea solution suction pipe are inserted into the inner pipe.
Korean Patent No. 1020120119470 discloses a sensor unit for a urea tank with a return pipe for defrosting frozen water. The unit rapidly defrosts the frozen water without driving an engine by having a heating cable and filler in a space between the inner and outer pipes of a dual pipe unit. The sensor unit for a urea tank with a return pipe for defrosting frozen water comprises a head, a lead pipe, a heating pipe, a urea suction pipe, a urea return pipe, and a float. A plurality of nozzle holes is formed on the outer surface of the return pipe, and discharges the urea to the urea tank. The nozzle holes are connected to an inner fluid path. The float is coupled to the outer diameter of the lead pipe, and slides up and down according to the amount of the urea in the urea tank.
Japanese Patent No. 2010216306 discloses an aqueous urea tank for a vehicle for use in an exhaust emission control device. The aqueous urea tank has a cooling water pipe through which engine cooling water flows. The tank further has an aqueous urea pipe to suck in the aqueous urea and send it to an aqueous urea SCR system. The cooling water pipe is furnished partially with an aqueous urea heating pipe structured so that a flow passage is formed in a large diameter pipe in a space with respect to its inner wall and a small diameter pipe is provided internally, wherein one of the pipes is used as aqueous urea pipe while the other is used as the heating water pipe. A suction hole at the tip of the first pipe is located near the bottom in the tank body so as to suck in the aqueous urea solution. The aqueous urea solution flowing through this pipe is heated by the engine heating water flowing through the other pipe.
PCT Application No. 2011078692 discloses an apparatus for measuring quality of a urea solution which is operated with at least a portion of the apparatus inserted into the urea solution. The apparatus includes a configuration of sensors for measuring mechanical and electrical properties within a volume of the urea solution, the measurements of mechanical and electrical properties being mutually differently influenced by components present in the urea solution. A data processing arrangement of the apparatus processes the measurements of mechanical and electrical properties for generating output data indicative of a quality of the urea solution. The apparatus is also capable of being adapted to measure qualities of other types of solution.
There is a need to improve operation of the suction-return under cold conditions.